In discussion on  issue 699671 , it became more clear that users may need to group flakes together in various ways depending on the flakes involved. To address this need, we should provide users an ability to specify custom rules that would take priority over default grouping. The rules will be specified as a set of regular expressions for master, builder, step and test name. The app should check newly-detected flake against all these rules and if any rule matches, it should report new flakes on a single issue corresponding to the rule.

Related is the issue 576274, where we try to change the default behavior currently used to group issues together.